This section is from the book "A Text-Book Of Materia Medica And Pharmacy For Medical Students", by Velyien Ewart Henderson. Also available from Amazon: A Text-Book of Materia Medica and Pharmacy for Medical Students.
Emulsions. These are mixtures of resinous or oily substances with water. They consist of minute particles of the active substance surrounded with, kept apart, and in suspension by means of mucilage made from one of the gums. Acacia or Tragacanth are commonly selected in the dispensary. Perfect natural emulsions are to be seen in milk and in the yolk of egg.
Of the resinous drugs Asafetida, Myrrh, Copaiba, Extract of Male Fern, the Tinctures of Cannabis Indica, Tolu, the Compound Tinctures of Guaiacum, and Benzoin, frequently require treatment, as do Cod-Liver and Castor Oils, Turpentine and Camphor. In the case of the gum-resins such as Asafetida which contains a good deal of gummy matter it is not necessary to add extraneous gum to obtain an emulsion, that which is part of the drug being sufficient on trituration with water.
Emulsions are prepared with the aid of a mortar and flat pestle. A thick mucilage is first made and with constant stirring a portion of the drug is added in small quantities until the emulsion is obtained, when the balance is added alternately with the remaining water in successive portions until the whole is emulsified.
With oils a second method may be adopted, called the English Method. Two or three parts by weight of Gum Acacia are triturated in a mortar with eight parts of Oil until the gum is completely suspended. Then one and a half parts of Water are added at once when a few revolutions of the pestle will secure an emulsion. The balance of the Water is now to be added in successive quantities until the whole is used. If the emulsion is not completed in the first stage of the process or the water is added too freely the oil separates and the emulsion is said to "crack" and cannot be restored.
On the Dispensing of Pills. The prerequisite of a properly made pill is a proper pill mass. This should possess the following characters, consistence, cohesiveness, and plasticity. Proper consistence is essential for if too hard the mass may not be divided into pills while if too soft the pills made will not retain their shape and will tend to run together. In dispensing a pill, the ingredient present in smallest amount and especially if it is very potent, is first tritrated in the mortar with a gradually increasing quantity of one of the other ingredients. All the other ingredients are ground together to a thoroughly smooth impalpable powder before the excipient is added. After the excipient has been thoroughly ground up and mixed with other ingredients (the mortar and pestle should be scraped down several times with a stiff-bladed metal spatula during the process) the mass is scraped together and transferred to the pill machine or is rolled in the hands into a smooth ball, then on the pill tile into a pipe, which must be kept of the same bore throughout its length. By constant rolling the pipe (after its ends have been squared by pressure) is made to reach the length indicated on the tile for the required number of pills. It is then cut into pill lengths as shown on the tile and each length carefully rounded on the hand or tile with the finger tips. When all the pills are rounded they may be finished by placing them under the pill finisher with a little dusting powder. The finisher is made to describe a figure-of-eight movement until the pills are round.
Pills must be round, not cracked, and not sticky. If stickiness develops during rolling, a dusting powder, starch, talc, or powdered liquorice, may be used on hands and tile.
Excipients must be added slowly and only as much as is needed. Fluid excipients should be dropped first on the spatula and added only one drop at a time.
The following are some of the most useful excipients:-
Of use where there are considerable proportions of aqueous extracts as those of Aloes, or Cascara; where there is a gummy substance as Asafetida, or with those holding Hard Soap.
One of the best for general use, being powerfully adhesive, at the same time preserving the consistence of the pill and promoting its solution. Tragacanth has large powers for absorbing water.
Much used in the official pills and particularly where it is not necessary to confer much adhesiveness to the mass.
Makes a good excipient for general use, not being eligible of course in those pills where vegetable substances are to be avoided as with pills of Silver Nitrate.
These possess mild adhesiveness. The former because of its absorbent power is useful with very soft masses, it also makes an excellent dusting powder for the finished pills.
The former is of use in making those pills containing vegetable substances as powdered crude drugs, the extracts, and the gum resins such as Myrrh or Asafetida. The latter is especially helpful with pills of Creosote or the Essential Oils. Avoid using soap for massing metallic salts, acids, or compounds of Tannin.
Of use in massing easily combustible substances such as Permanganate of Potassium. Nitrate of Silver and Phosphorus. Cohesion is secured by the addition of a fatty substance such as Resin Ointment.
Is mentioned only that it may be avoided unless combined with some fibrous powder as Licorice or Althaea Powder. Pills made with Acacia are apt to become extremely hard and have been known to pass through the bowel undissolved.
For the physician to attempt anything more than a simple dusting of new made pills with some inert dry powder such as Licorice would be to tempt disaster as the process of coating with sugar, silver, or gelatin, other than using a gelatin capsule, belongs to the expert dispenser. Pills intended for solution in the bowel may be coated with a preparation of Keratin in which case they must be made with a fatty exci-pient, and are difficult to make. They also may be coated with melted Salol which is placed in a shallow container and the pills rotated in it until covered. If Salol is used the excipient must not be made of fat.